The invention concerns a nuclear magnetic resonance (=NMR) probehead, comprising N basic elements, where N≧2, wherein each basic element comprises a measurement sample and a resonator system, and wherein the N resonator systems of the N basic elements are coupled to each other.
Such an NMR probehead is known, for example, from US 2006/0164088 A1, according to US 2006164088.
NMR spectroscopy is a powerful method of instrumental analysis. Radio-frequency (RF) pulses are radiated into a sample to be examined, which is located in a strong, static magnetic field B0, and the reaction of the sample is measured. The chemical bond relationships in the probe can be inferred from the position and intensity of NMR lines.
The RF radiation is transmitted and received by means of RF resonators. The RF resonators are located in the immediate vicinity of the sample or the sample is located inside the RF resonators.
The quality of NMR measurement depends on the signal-to-noise ratio (SNR) that can be achieved. The SNR depends, among other factors, on the RF resonators used. A number of measures are known by which a good SNR can be achieved:
Especially high filling factors can be achieved by the use of toroid resonators (see U.S. Pat. No. 5,045,793, U.S. Pat. No. 6,788,064, U.S. Pat. No. 5,574,370, and “Computing the B1 field of the toroidal MRI coil” Butterworth and Gore, J. Magn. Reson. 175, 114-123 (2005)). With toroid resonators, however, inhomogeneities of the static magnetic field cannot be fully compensated for by “shimming”. Moreover, these resonators exhibit an extremely inhomogeneous RF field, so that the high filling factor cannot be utilized.
Furthermore, lossy samples often have to be measured; RF radiation is heavily absorbed, especially, by water or saline, acid or base solutions (which are often used as solvents for the substance to be measured). The SNR can then be improved by a sample that is thin in the direction of the electrical field (E-field) component of the RF radiation which is positioned in the region of the passage through zero of the E-field (see U.S. Pat. No. 7,068,034 and U.S. Pat. No. 6,917,201).
U.S. Pat. No. 5,003,265 discloses an NMR tomograph in which an RF coil has a plurality of consecutive, spaced, inductively coupled, ring-shaped resonators. The resonators together enclose a measurement volume to be imaged.
US 2004164738, WO 00 50924, U.S. Pat. No. 4,654,592, U.S. Pat. No. 6,456,072, US 2005253587, and US 2006164088 disclose that a plurality of measurement samples, each in a separate detection coil, can be placed in an NMR probehead. The samples are then measured individually. This method is intended to minimize the time for placing samples in the probehead and for field homogenization. In this case, the samples usually contain different substances to be measured and are analyzed separately.
The object of this invention is to present an NMR probehead, with which an improved SNR can be achieved with lossy samples.